The technology of mobile phones has made possible mobile voice communication for millions of people. Mobile phones are carried and used daily by hundreds of millions of people and become an ordinary household items worldwide. The mobile phone user quite often makes the phone call while driving an automobile and therefore creates a potential hazardous driving condition since the driver has to hold the mobile phone and drive at the same time.
A hand-free kit is an external accessory to the mobile phone and its purpose is to free the driver from distraction of holding and using the mobile phone. Several technologies have been pursued to enable the driver to use the mobile phone without holding the cellular phone.
U.S. Pat. No. 6,134,456 discloses a control switch box with cables linking the mobile phones and the vehicular stereo system. However, installating such kind of accessory is quite involved and requires wiring and routing inside the automobile body.
The U.S. Pat. No. 5,867,794 discloses another method that uses an FM transmitter to send the audio signal from the mobile phone to the vehicular FM radio. In the disclosure, there is no need to physically connect the mobile phone and the vehicular audio system. However, the disadvantage of this approach is that the frequency of the FM transmitter has to be set to the same channel as the FM radio receiver that the driver is currently listening to whenever he wants to use the hand-free kit. The frequency of either the FM transmitter or the FM radio receiver has to be adjusted and it causes much inconvenience in application.
It will be an innovative approach to include an apparatus or a method to detect radio frequency of the FM radio receiver and to set the frequency of the FM transmitter automatically.